In recent years, there have been an increasing demand for flat display devices (flat panel displays), such as, for example, a liquid crystal display device and the like, and flat display devices have been widely used for mobile devices, such as smart phones, mobile phones, and the like.
For example, a liquid crystal display device includes a back light unit serving as a light device and a liquid crystal display panel disposed so as to face the back light unit. The back light unit includes a light source, such as a light emitting diode (LED) and the like, and a flexible printed circuit board (FPC) for supplying a light source signal and the like to the light source. The liquid crystal display panel includes a TFT substrate on which a plurality of thin transistors (TFTs) are formed and an FPC for supplying a control signal to the TFT substrate. That is, each of the back light unit and the liquid crystal display panel includes an FPC.
Also, in recent years, the function of display devices is increased by superimposing not only a back light unit but also, for example, a so-called touch panel, a parallax barrier panel for performing a stereoscopic image display, and the like, on a liquid crystal display panel.
However, since each of the touch panel, the parallax barrier panel, and the like, includes an FPC and, normally, a connector is provided in each of the FPCs, not only a relatively large space has to be provided in order to dispose the connecters but also the component cost is increased because of the connectors themselves.
Patent Document 1 discloses that, in a display device which includes a liquid crystal display panel, a back light unit, and a touch panel, to a first FPC of the liquid crystal display panel, bonded are a second FPC of the touch panel and a third FPC of the back light unit by solder connection or anisotropic conductive film (ACF) connection. Thus, the connectors of the second and third FPCs are omitted and the connector of the first FPC is shared by the FPCs, thereby reducing the number of connectors and thus solving the problem relating to the space for connectors and the component cost.